Two catastrophes have been in the making since President Bush and Tony Blair launched their war on Iraq four years ago. Both are epoch-making, and their resolution will shape regional and world politics for decades to come.

The first catastrophe relates to the political and moral consequences of the war in the US and UK, and its resolution is the urgent task facing the American and British peoples. The second concerns the devastation wrought by the war and subsequent occupation, and the lack of a unified political movement within Iraq that might overcome it.

Bush and Blair are in a state of denial, only offering us more of the same. They allegedly launched the war at first to save the world from Saddam's WMD, then to establish democracy, then to fight al-Qaida's terrorism, and now to prevent civil war and Iranian or Syrian intervention.

Four years after declaring "mission accomplished", the US government is sending more combat troops to add to the bloodbath - all in an effort to impose its imperial will on the Iraqi people, and in the process plunging its own country into its deepest political-moral crisis since Vietnam. Under heavier pressures, Blair, the master of tactical subterfuge, is redeploying Britain's forces within Iraq and Afghanistan, under the guise of withdrawal. He has long known that British bases in Basra and the south were defenceless against attacks by the Sadr movement and others.

Bush, on the other hand, is escalating Iraq's conflict and threatening to launch a new war, this time against Iran. It is hard not to presume that what he means by an exit strategy is to install a client regime in Baghdad, backed by US bases. The Iraqi people will not accept this, and the west should be alerted to the fact that US policy objectives will only lead to wider regional conflicts, rather than to full withdrawal.

In attempting to achieve their objective, the occupation forces will escalate their war with the resistance forces within and north of Baghdad, as well as clashing with the popular Sadr movement in the capital and the south. The latter is, despite the ceasefires and political manoeuvrings, Iraq's biggest organised opposition force to the occupation.

Meanwhile, the destruction of Iraq continues apace and its people are subjected to levels of sustained violence unknown in their history. Overwhelmingly, the violence is a direct or indirect product of the occupation, and the bulk of sectarian violence is widely known in Iraq to be linked to the parties favoured by Washington. For example, forces in control of the various ministries, including the interior ministry, clash regularly.

It is not difficult to see how this violence is linked to the occupation, for it has spawned a multitude of violence-makers: 150,000 occupation forces; 50,000 and rising contracted foreign "mercenaries"; 150,000 Iraqi Facilities Protection forces, paid by the Iraqi regime, controlled by the occupation and engaged in death-squad activities, according to the prime minister, Nuri al-Maliki; 400,000 US-trained army and police forces; six US-controlled secret Iraqi militias; and hundreds of private kidnap gangs. Pitted against some or all of these are tens of thousands of militias and resistance forces of various political hues. In total there are about 2 million actively organised armed men in the country. There are about 3,000 attacks on occupation forces every month, while tens of thousands of Iraqis languish in prison, where torture is widespread and trials considered an unnecessary formality.

The success of the occupation's divide-and-rule tactics and their insistence on basing the new political and military structures on sects, religions, and ethnicities is threatening the communal cohesion that was once the country's hallmark. This is a factor in the absence of a united movement, capable of leading the struggle to end the occupation. The occupation has sown divisions where there were none and transformed existing differences into open warfare.

And is it any wonder that the long-suffering Iraqi people find themselves at an impasse. Try catching your breath after decades of brutal dictatorship, 13 years of economic sanctions and four years of an obscene war .

But even in the absence of a unified anti-occupation front, the resistance of the Iraqi people has managed to thwart the world's greatest military empire. And there are signs of a mass rejection of these sectarian forces, and the possibility that public anger will translate into the very unity that is so desperately needed. Rage against corruption and the collapse of public services is sweeping the country, including Kurdistan. Similarly, the proposed corporate occupation of Iraq, disguised as a legal document to tie the country to the oil companies for decades to come, has reminded the population of one of the main reasons for the US-led invasion. It has also reminded them what a self-respecting, sovereign Iraq looked like in 1961, when the government nationalised Iraq's lands for future oil production.

In an opinion poll released by the BBC yesterday, 86% of people are opposed to the division of Iraq. This and other polls also show majority support for armed resistance to the occupation. Four years into this terrible adventure, both the US and Britain must realise that it is time to pack up and leave.

· Sami Ramadani was a political exile from Saddam's regime and is a senior lecturer at London Metropolitan University.